A multi-antenna mobile communication system is a system that has the merit of sending a large amount of data at a high speed by an increase of the entire data throughput by configuring multiple antenna paths.
In order to maximize the performance of the multi-antenna mobile communication system, an error of the phase and gain properties of multiple RF paths should be efficiently calibrated.
FIG. 1 is an explanatory view illustrating a conventional RF path calibration method for a multi-antenna mobile communication system.
As shown in FIG. 1, the conventional RF path calibration of the multi-antenna mobile communication system is divided into transmission RF path calibration and reception RF path calibration.
First, in the transmission RF path calibration method, a transmission signal from a baseband modem unit or calibration unit is coupled at the front end of an antenna and down-converted, and then a change in the phase and amplitude of an RF transmission path is calculated by using the correlation between the down-converted transmission signal and the original transmission signal.
That is, when an IF transmission signal from a digital IF 105 or baseband modulator 107 is transmitted to an antenna 101 through an RF transmission path, a coupler 102 at the front end of the antenna 101 couples the RF transmission signal to deliver the same to an RF calibration up/down converter 115.
Then, the RF calibration up/down converter 115 converts (down-converts) the RF transmission signal back to an IF transmission signal so as to be processed in the baseband, and then applies the same to a calibrator 116 in the baseband.
The calibrator 116 detects any change in the phase and gain of the RF transmission path by an operation of cross correlation of the IF transmission signal inputted from the RF calibration up/down converter 115 and the IF transmission signal from the digital IF 105 or the baseband modulator 107.
A transmission RF path calibration is performed by the above procedure.
Next, in a reception RF path calibration method, a test vector or test signal from a baseband modem unit or calibration unit is up-converted by the RF calibration up/down converter 115, and then received through a reception RF path, wherein a change in the phase and amplitude of the RF reception path is calculated by using the correlation with the original test signal.
That is, the RF calibration up/down converter 115 converts a test signal from the calibrator 116 into an RF test signal, and then inputs the same to the RF reception path simultaneously through a switch 113, a circulator 114, and a divider 112.
The RF test signal so inputted is down-converted through an RF receiver, and then inputted to a baseband demodulator 106. At this time, the calibrator 116 detects any change in the phase and gain of the RF reception path by an operation of cross correlation of the test signal transmitted at the initial stage and the RF test signal passed through the RF reception path.
The error of the RF transmission and reception phase and gain thus detected is reflected in the procedure of generating a transmission signal by the modulator 107 and the demodulator 106, and upon reception, it is reflected in the procedure of demodulation.
The aforementioned conventional method has a problem in that the calculation amount of the baseband modulator and of the demodulator is remarkably increased because an error of the RF transmission and reception paths is calculated in the baseband, and the hardware complexity of the system is increased due to an increase of the interface among the modulator, the demodulator, and the calibrator.
In addition, the conventional method has a shortcoming that an additional RF up/down converter for up/down converting a transmission signal and a test signal is required because RF transmission and reception errors are calibrated in the baseband, and additional RF parts, such as the switch, the divider, the circulator, etc. are required at the front end of the RF antenna.
Further, the conventional method is problematic in that the flexibility of the baseband system is reduced because an error of the RF path is calibrated by using a special test signal in the baseband, and there is a limit in the establishment of a system having an excellent expandability.